2017 IMO Problem #5

Combinatorics
Alex Ferguson
Math

[robertoroma]

Amazing solution! I love your accent, you kind of sound like that Gary Kasparov clip where he shows a king and pawn endgame and then says: “boom, white lost, yes?” Keep up with the great work!

[irhamma]

I am so wondering about a few things :
1. If we number them from 1 to n(n+1)
Then we remove the n(n-1), then we make them closer all together, then we get the remaining players of order : a_1 < a_2 < ... < a_2n.
Is it?
2. Does the main idea suggests that we need to prove that, out of n(n+1) we can obtain 2n players with height sequence is either increasing or decreasing?